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HAW THORNE
fields were unequal, both among years and harvests. This finding nullified predicting alfalfa production from intermittent harvests during a
growing season. Measurements of production are required for all har-
vests in a Study period.
The amounts of “Sr and of °"Cs associated with alfalfa in each field
were computed with the same equation used for computing soil fission
products. The same uncertainties apply to the meanvalue as a descrip-
tion of the amounts of "Sr and of "Cs with a crop as were given
earlier for the radionuclide content of the soils of the fields. Compo-
nents of variances are as intricately intertwined between the dependent
variable and the independent variables as they were for soils. Again,
there is a confounding of the real variation in fission-product distribution in Space with variation introduced by sampling and analytical procedures.
Measures of the variability of a material maybe expressed in several forms. In Fig. 8 the mean production of alfalfa is indicated for one
field with the dispersion among square-meter specimensillustrated as
plus or minus one Standard deviation. As expected, the weight of alfalfa
varies with the season of the year and from year to year. In addition,
the reliability with which the means can be defined also varies among
the harvests.
The points of greatest interest in studies of a dairy farm are those
where man becomes a consumer of the farm products. Figure 9 illustrates the variation of "cs and Sr per unit volume of milk over a
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' Fig. 8—-Mean weight of alfalfa samples, with dispersion among specimen weights characterized by one standard deviation, in harvests from
one field during three growing seasons.